The present invention provides an improved filter, and improved method, for purifying molten magnesium and magnesium alloys.
Magnesium and magnesium alloys are widely used and there are considerations for further use as a strong, light-weight, material in any application where these properties are advantageous. As would be realized, the use of magnesium requires purification to remove oxides, inter-metallic insoluble inclusions and other particles which could degrade the quality of a casting or ingot use for further downstream fabrication. Avoiding formation of such impurities has never been perfected, therefore the need for a removal method remains.
Filtration of molten metals through reticulated foam is widely practiced with each type of metal requiring filters constructed of specific materials. Molten aluminum and aluminum alloys are typically filtered by a reticulated foam filter comprising aluminum phosphate bonded alumina, sinter bonded high purity alumina or sinter bonded alumina-mullite. Molten copper and copper alloys are typically filtered through silica-bonded silicon carbide, aluminum phosphate bonded silicon carbide, sinter bonded alumina-mullite, sinter bonded magnesium oxide partially stabilized zirconia and yttria partially stabilized zirconia-alumina. Molten iron and many iron alloys are typically filtered with silica bonded silicon carbide, aluminum phosphate bonded silicon carbide, mullite or cordierite-mullite. Nickel-based superalloys are typically filtered with sinter bonded high purity alumina or sinter bonded partially stabilized zirconia. Steel, such as stainless steel, is typically filtered through partially stabilized zirconia.
Magnesium and magnesium alloys are typically filtered through reticulated foams of sinter bonded high purity alumina, sinter bonded magnesia, sinter bonded magnesium oxide partially stabilized zirconia or magnesium aluminate spinel. Molten magnesium and its alloys readily wet and chemically attack refractory oxide materials including high purity sinter bonded alumina, sinter bonded magnesia and sinter bonded magnesia partially stabilized zirconia. Other materials such as alumina, magnesia, magnesium aluminate spinel and zirconia are also readily wetted and chemically attacked by molten magnesium and its alloys making them unsuitable for use.
Due to the effective wetting and chemical attack on many materials the art has been lacking a suitable material for filtering molten magnesium or magnesium alloys. The present application provides a material, which is suitable for filtering molten magnesium and magnesium alloys.